The present invention relates to a paper tractor for feeding paper, especially fanfold paper, in a printer.
Prior sheet feeders in printers are constructed to feed various types of print paper such as individual sheets and continuous paper. One conventional sheet feeder for feeding continuous paper, particularly fanfold paper, having feed holes on both sides thereof, comprises a cylindrical platen for winding the paper partically therearound, a guide shape extending parallel to the platen, and a pair of pin tractors supported on the guide shaft. The pin tractors have a plurality of pins for fitting in the feed holes in the fanfold paper. The pins on the pin tractors are rotated when the guide shaft is rotated, thereby moving and feeding the paper. There are two types of paper feeding known in the art. The first paper feeding type is such that the paper is pulled by the pin tractors to move in a path below and then over the platen and through the pin tractors. According to the second paper feeding type, the paper is pushed by the pin tractors to move in the path through a pin tractors and then below and over the platen. Each of these paper feeding types can be employed for feeding paper of various widths since the pin tractors are movable parallel to the guide shaft.
However, the paper-pulling pin tractors have been disadvantageous in that the pin tractors and the guide shaft tend to interfere with the fanfold paper as it is set in place. The use of the pin tractors results in a complex printer which cannot be reduced in size.
The paper-pushing pin tractors also suffer from the above difficulties, and have additional problems in that the paper will not be fed accurately and printed images are liable to become distorted when a graphic pattern is printed in a dot printer.
Another known paper tractor has a cylindrical platen for winding paper partically therearound and a pair of pin wheels fixed to the opposite ends of the platen. The pin wheels have a plurality of pins for fitting in feed holes defined in the opposite sides of paper. Since the pin wheels rotate with the platen, the paper can be fed accurately to feed the paper line-by-line in alignment with the line position which is printed. This known paper tractor mechanism is simpler and smaller than the system having the pin tractors. However, because the pin wheels are spaced at a fixed interval, the width of the paper that can be used is limited.
Recent printers are required to be able to feed the paper accurately in forward and reverse directions for graphic and color printing operations, for example. There is a demand for a paper feeder capable of feeding print paper of different widths and of feeding the print paper highly accurately.